FIGS. 3(a) and 3(b) are schematic diagrams showing a conventional process of epitaxial growth of GaAs by MOCVD. In FIGS. 3(a) and 3(b), reference numeral 1 designates a GaAs substrate, reference numeral 2 designates Ga atoms, reference numeral 3 designates As atoms, and reference numeral 4 designates Si atoms. In the MOCVD method, trimethylgallium (TMG) is used as a source of Ga and arsine (AsH.sub.3) is used as a source of As. When Si is used as a dopant, silane (SiH.sub.4) is used.
FIG. 3(a) shows a growth process without dopant impurities and a three-dimensional growth in which Ga atoms and As atoms are alternately deposited is carried out.
FIG. 3(b) shows a growth process Si atom 4 is a dopant impurity. In this case, impurity element Si is supplied at the same time when main elements Ga and As for constituting a crystal are supplied, whereby the electric conductivity of crystal, that is, n type or p type is controlled.
In the prior art crystal growth method constituted as described above, the main element and the impurity are supplied at the same time thereby to control the electrical conductivity type. When IV group element is supplied as impurity in a III-V compound semiconductor, Si as a IV group element replaces either Ga atom as III group element or As atom as V group element as shown in FIG. 3(b). In the former case, Si behaves as a dopant showing n type conductivity (generally called a "donor") and in the latter case, Si behaves as a dopant showing p type conductivity (generally called an "acceptor"). In other words, Si behaves as an amphoteric impurity. In the MOCVD method, however, doping with Si produces n type conductivity and even doping with Ge which is also IV group element produces n type conductivity. In this way, in the supply of impurities in the prior art crystal growth method, although the impurity is an amphoteric impurity, the conductivity type is determined unconditionally and doping control sufficiently utilizing the properties of the impurity is not achieved.